Fuser coating composition and method of manufacture

ABSTRACT

The present teachings include a coating composition which includes a liquid, fluoropolymer particles, carbon nanotubes, and a dispersant. The dispersant has a thermal degradation temperature below the melting temperature of the fluoropolymer particles.

BACKGROUND

1. Field of Use

This disclosure is generally directed to fuser members useful inelectrophotographic imaging apparatuses, including digital, image onimage, and the like. This disclosure also relates to processes formaking and using fuser members.

2. Background

In a typical electrophotographic imaging apparatus, an image of anoriginal to be copied, or the electronic document image, is recorded inthe form of an electrostatic latent image upon a photosensitive memberand the latent image is subsequently rendered visible by the applicationof thermoplastic resin particles or composites thereof which arecommonly referred to as toner. The visible toner image is in a loosepowdered form and can be easily disturbed or destroyed. The toner imageis usually fixed or fused upon a substrate or support member supportwhich may be a cut sheet or continuous media, such as plain paper.

The use of thermal energy for fixing toner images onto a support memberis well known. In order to fuse toner material onto a support surfacepermanently by heat, it is necessary to elevate the temperature of thetoner material to a point at which the constituents of the tonermaterial coalesce and become tacky. This heating causes the toner toflow to some extent into the fibers or pores of the support member.Thereafter, as the toner material cools, solidification of the tonermaterial causes the toner material to be firmly bonded to the support.

Several approaches to thermal fusing of toner images have been describedin the prior art. These methods include providing the application ofheat and pressure substantially concurrently by various means: a rollpair maintained in pressure contact; a belt member in pressure contactwith a roll; and the like. Heat may be applied by heating one or both ofthe rolls, plate members or belt members. The fusing of the tonerparticles takes place when the proper combination of heat, pressure andcontact time is provided. The balancing of these parameters to bringabout the fusing of the toner particles is well known in the art, andcan be adjusted to suit particular machines or process conditions.

During operation of a fusing system in which heat is applied to causethermal fusing of the toner particles onto a support, both the tonerimage and the support are passed through a nip formed between the rollpair, or plate or belt members. The concurrent transfer of heat and theapplication of pressure in the nip affect the fusing of the toner imageonto the support. It is important in the fusing process that no offsetof the toner particles from the support to the fuser member take placeduring normal operations. Toner particles that offset onto the fusermember may subsequently transfer to other parts of the machine or ontothe support in subsequent copying cycles, thus increasing the backgroundor interfering with the material being copied there. The referred to“hot offset” occurs when the temperature of the toner is increased to apoint where the toner particles liquefy and a splitting of the moltentoner takes place during the fusing operation with a portion remainingon the fuser member. The hot offset temperature or degradation to thehot offset temperature is a measure of the release property of the fusermember, and accordingly it is desirable to provide a fusing surface,which has a low surface energy to provide the necessary release.

A fuser or image fixing member, which can be a rolls or a belt, may beprepared by applying one or more layers to a suitable substrate.Cylindrical fuser and fixer rolls, for example, may be prepared byapplying an elastomer or fluoroelastomer to an aluminum cylinder. Thecoated roll is heated to cure the elastomer. Such processing isdisclosed, for example, in U.S. Pat. Nos. 5,501,881; 5,512,409; and5,729,813; the disclosure of each of which is incorporated by referenceherein in their entirety.

Fuser members may be composed of a resilient silicone layer with afluoropolymer topcoat as the release layer. Fluoropolymers can withstandhigh temperature (>200° C.) and pressure conditions and exhibit chemicalstability and low surface energy, i.e. release properties. For instance,fluoroplastics, such as TEFLON® from E.I. DuPont de Nemours, Inc. have alower surface energy due to high fluorine content and are widely usedfor oil-less fusing.

Fluoroplastics, such as PTFE and PFA, can be applied by coatingtechnique onto a fuser member substrate to form a release layer. Sincefluoroplastics typically require high baking temperatures (i.e. over300° C.) to form a continuous film, which is well above thedecomposition temperature of silicone rubber (about 250° C.), theprocessing window for forming a fluoroplastic topcoat over asilicone-containing substrate to achieve uniform coatings withoutdefects is extremely narrow. Cracks and bubbles are the two majordefects observed during the fabrication of such fuser members.

SUMMARY

According to various embodiments, the present teachings include acoating composition which includes a liquid, fluoropolymer particles,carbon nanotubes, and a dispersant. The dispersant has a thermaldegradation temperature below the melting temperature of thefluoropolymer particles.

An alternate embodiment includes a method of making a fuser member. Themethod includes obtaining a fuser member, including a silicone resilientlayer disposed on a substrate. The method includes providing a coatingdispersion, which includes a liquid, fluoropolymer particles, carbonnanotubes, and a dispersant. The dispersant has a thermal degradationtemperature below the melting temperature of the fluoropolymerparticles. The coating dispersion is applied over the silicone resilientlayer to form a coating layer. The coating layer is heated to atemperature above the degradation temperature of the dispersant to allowremoving the dispersant to form a fuser member.

A further aspect described herein is a fuser member that includes asubstrate, a silicone layer disposed on the substrate, and an outerlayer disposed on the silicone layer. The outer layer is formed from acoating dispersion comprised of a liquid, fluoropolymer particles,carbon nanotubes, and a thermally removable dispersant, wherein thethermally removable dispersant has a thermal degradation temperaturebelow the melting temperature of the fluoropolymer particles.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of thepresent teachings and together with the description, serve to explainthe principles of the present teachings.

FIG. 1 is a schematic illustration of an image apparatus.

FIG. 2 is a schematic of an embodiment of a fuser member.

FIG. 3 is a photographic of a fluoroplastic topcoat containing cracksand bubbles.

FIG. 4 shows tensile strain versus tensile stress for fluoroplastictopcoat (a) without carbon nanotubes and (b) with carbon nanotubes.

It should be noted that some details of the drawings have beensimplified and are drawn to facilitate understanding of the embodimentsrather than to maintain strict structural accuracy, detail, and scale.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to embodiments of the presentteachings, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

In the following description, reference is made to the accompanyingdrawings that form a part thereof, and in which is shown by way ofillustration specific exemplary embodiments in which the presentteachings may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice thepresent teachings and it is to be understood that other embodiments maybe utilized and that changes may be made without departing from thescope of the present teachings. The following description is, therefore,merely exemplary.

Referring to FIG. 1, in a typical electrostatographic reproducingapparatus, a light image of an original to be copied is recorded in theform of an electrostatic latent image upon a photosensitive member andthe latent image is subsequently rendered visible by the application ofelectroscopic thermoplastic resin particles, which are commonly referredto as toner. Specifically, a photoreceptor 10 is charged on its surfaceby means of a charger 12 to which a voltage has been supplied from apower supply 11. The photoreceptor 10 is then imagewise exposed to lightfrom an optical system or an image input apparatus 13, such as a laserand light emitting diode, to form an electrostatic latent image thereon.Generally, the electrostatic latent image is developed by bringing adeveloper mixture from a developer station 14 into contact therewith.Development can be effected by use of a magnetic brush, powder cloud, orother known development process. A dry developer mixture usuallycomprises carrier granules having toner particles adheringtriboelectrically thereto. Toner particles are attracted from thecarrier granules to the latent image, forming a toner powder imagethereon. Alternatively, a liquid developer material may be employed,which includes a liquid carrier having toner particles dispersedtherein. The liquid developer material is advanced into contact with theelectrostatic latent image and the toner particles are deposited thereonin image configuration.

After the toner particles have been deposited on the photoconductivesurface in image configuration, they are transferred to a copy sheet 16by a transfer means 15, which can be pressure transfer or electrostatictransfer. Alternatively, the developed image can be transferred to anintermediate transfer member, or bias transfer member, and subsequentlytransferred to a copy sheet. Examples of copy substrates include paper,transparency material such as polyester, polycarbonate, or the like,cloth, wood, or any other desired material upon which the finished imagewill be situated.

After the transfer of the developed image is completed, copy sheet 16advances to a fusing station 19, depicted in FIG. 1 as a fuser roll 20and a pressure roll 21 (although any other fusing components such asfuser belt in contact with a pressure roll, fuser roll in contact withpressure belt, and the like, are suitable for use with the presentapparatus), wherein the developed image is fused to copy sheet 16 bypassing copy sheet 16 between the fusing and pressure members, therebyforming a permanent image. Alternatively, transfer and fusing can beeffected by a transfix application.

Photoreceptor 10, subsequent to transfer, advances to cleaning station17, wherein any toner left on photoreceptor 10 is cleaned therefrom byuse of a blade (as shown in FIG. 1), brush, or other cleaning apparatus.

FIG. 2 is an enlarged schematic view of an embodiment of a fuser member,demonstrating the various possible layers. As shown in FIG. 2, asubstrate 25 has an intermediate layer 22 thereon. Intermediate layer 22can be, for example, a silicone rubber. On intermediate layer 22 is anouter layer 24, for example, a fluoroplastic.

Fluoroplastics have been used as the topcoat materials for oil-lessfusing for their good releasing property. PFA and PTFE, the mostrepresentative fluoroplastics for fusing applications, are chemicallyand thermally stable and possess a low surface energy. However, thesematerials are also highly crystalline and therefore difficult toprocess. High temperature sintering (>350° C.) is the only way to makethem into a continuous film. The silicone rubber layer starts to degradearound 250° C. It is theorized that while melting the topcoats attemperatures greater than 300° C., the silicone rubber releases gas orsmall molecules. This creates cracks or bubbles in the topcoat layer asshown in FIG. 3. The cracks and bubbles formed in the fluoroplasticsurface layer coatings are caused by the silicone rubber degradationwhile baking the fluoroplastic surface layer at high temperatures. Therequired baking temperature for PFA is over 320° C., which is well abovethe decomposition temperature of silicone rubber (about 250° C.). Whenthe decomposed materials release during the formation of thefluoroplastic surface layer, cracks or bubbles are formed. The currentfluoroplastic coating formulations provide an extremely narrowprocessing window to achieve a defect-free fluoroplastic topcoat. Themanufacturing yield of the fluoroplastic fuser topcoats is very low.

An exemplary embodiment of a topcoat formulation that prevents cracksand bubbles from forming includes a liquid, fluoropolymer particles,carbon nanotubes (CNT) and a stabilizer or dispersant that decomposes ata temperature below the melting temperature of fluoropolymer particles.The selected decomposition temperature range of the stabilizer is fromabout 100° C. to about 280° C. In other embodiments, the decompositiontemperature range is from about 150° C. to about 260° C. or from about200° C. to about 260° C., or from about 230° C. to about 250° C. Thecombination of the CNT and the thermally removable stabilizer in theformulation are believed to help minimize cracks and bubbles in thetopcoat layer. Additionally, the stabilizer is removed by the thermalprocessing without negatively affecting the silicone rubber layer andthe PFA topcoat. The topcoat or release layer has an electrical surfaceresistivity of less than about 10⁸ Ω/sq.

The thickness of the outer fluoroplastic surface layer of the fusermember herein is from about 10 to about 250 micrometers, or from about15 to about 100 micrometers.

The silicone layer can include silicone rubbers such as room temperaturevulcanization (RTV) silicone rubbers, high temperature vulcanization(HTV) silicone rubbers, low temperature vulcanization (LTV) siliconerubbers and liquid silicone rubbers (LSR). These rubbers are known andreadily available commercially, such as SILASTIC® 735 black RTV andSILASTIC® 732 RTV, both from Dow Corning; and 106 RTV Silicone Rubberand 90 RTV Silicone Rubber, both from General Electric. Other suitablesilicone materials include the siloxanes (such aspolydimethylsiloxanes); fluorosilicones such as Silicone Rubber 552,available from Sampson Coatings, Richmond, Va.; liquid silicone rubberssuch as vinyl crosslinked heat curable rubbers or silanol roomtemperature crosslinked materials; and the like. Another specificexample is Dow Corning Sylgard 182.

The thickness of the silicone layer is from about 0.2 to about 20 mm, orfrom about 0.25 to about 7 mm.

Fluoropolymer particles suitable for use in the formulation describedherein include fluorine-containing polymers. These polymers includefluoropolymers comprising a monomeric repeat unit that is selected fromthe group consisting of vinylidene fluoride, hexafluoropropylene,tetrafluoroethylene, perfluoroalkylvinylether, and mixtures thereof. Thefluoropolymers may include linear or branched polymers, and cross-linkedfluoroelastomers. Examples of fluoropolymer includepolytetrafluoroethylene (PTFE); perfluoroalkoxy polymer resin (PFA);copolymer of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP);copolymers of hexafluoropropylene (HFP) and vinylidene fluoride (VDF orVF2); terpolymers of tetrafluoroethylene (TFE), vinylidene fluoride(VDF), and hexafluoropropylene (HFP); and tetrapolymers oftetrafluoroethylene (TFE), vinylidene fluoride (VF2), andhexafluoropropylene (HFP), and mixtures thereof. The fluoropolymerparticles provide chemical and thermal stability and have a low surfaceenergy. The fluoropolymer particles have a melting temperature of fromabout 255° C. to about 360° C. or from about 280° C. to about 330° C.

The liquid used as the media for the formulation can include water, analcohol, a C₅-C₁₈ aliphatic hydrocarbon such as pentane, hexane,heptane, nonane, dodecane and the like, a C₆-C₁₈ aromatic hydrocarbonsuch as toluene, o-xylene, m-xylene, p-xylene, and the like, an ether,an ester, a ketone, and an amide. The liquid provides a media fordispersion of fluoropolymer particles and the fillers.

As used herein and unless otherwise specified, the term “carbonnanotube” or CNT refers to an elongated carbon material that has atleast one minor dimension; for example, width or diameter of up to 100nanometers. In various embodiments, the CNT can have an average diameterranging from about 1 nm to about 100 nm, or in some cases, from about 10nm to about 50 nm, or from about 10 nm to about 30 nm. The carbonnanotubes have an aspect ratio of at least 10, or from about 10 to about1000, or from about 10 to about 100. The aspect ratio is defined as thelength to diameter ratio.

In various embodiments, the carbon nanotubes can include, but are notlimited to, carbon nanoshafts, carbon nanopillars, carbon nanowires,carbon nanorods, and carbon nanoneedles and their various functionalizedand derivatized fibril forms, which include carbon nanofibers withexemplary forms of thread, yarn, fabrics, etc. In one embodiment, theCNTs can be considered as one atom thick layers of graphite, calledgraphene sheets, rolled up into nanometer-sized cylinders, tubes, orother shapes.

In various embodiments, the carbon nanotubes or CNTs can includemodified carbon nanotubes from all possible carbon nanotubes describedabove and their combinations. The modification of the carbon nanotubescan include a physical and/or a chemical modification.

In various embodiments, the carbon nanotubes or CNTs can include singlewall carbon nanotubes (SWCNTs), multi-wall carbon nanotubes (MWCNTs),and their various functionalized and derivatized fibril forms such ascarbon nanofibers, as exemplarily shown in FIG. 1.

The CNTs can be formed of conductive or semi-conductive materials. Insome embodiments, the CNTs can be obtained in low and/or high puritydried paper forms or can be purchased in various solutions. In otherembodiments, the CNTs can be available in the as-processed unpurifiedcondition, where a purification process can be subsequently carried out.

The carbon nanotubes are present in an amount of from about 0.1 to about50 or from about 2 to about 20, or from about 5 to about 10 weightpercent based on the total weight of the carbon nanotube andfluoropolymer particles in the formulation.

The dispersant can include a polymeric amine, a polyethylene glycol, apolymeric acid, and a natural gum material. More specifically thedispersant can be a polyacrylic acid, a polymethacrylic acid, apolyethylene glycol containing surfactant, and a polyallylamine. Thedispersant is present in an amount ranging from about 1 weight percentto about 50 weight percent or from about 5 to about 30, or from about 10to about 20, based on the total weight of the carbon nanotubes and thedispersant in the formulation.

The Young's Modulus of the outer layer is from about 50 kpsi to about100 kpsi, or from about 70 kpsi to about 95 kpsi, or from about 85 kpsito about 95 kpsi. The tensile stress in the outer layer is from about1000 psi to about 5000 psi, or from about 2000 psi to about 4000 psi, orfrom about 2700 psi to about 3300 psi.

In various embodiments, the coating composition can be coated using, forexample, coating techniques, extrusion techniques and/or moldingtechniques. As used herein, the term “coating technique” refers to atechnique or a process for applying, forming, or depositing a dispersionto a material or a surface. Therefore, the term “coating” or “coatingtechnique” is not particularly limited in the present teachings, and dipcoating, painting, brush coating, roller coating, pad application, spraycoating, spin coating, casting, or flow coating can be employed.

EXAMPLES Example 1 General Procedure for Preparation of CNT/PFA Topcoatson Silicone Rubber Rolls

CNT aqueous dispersion: A surfactant solution is prepared by dissolvingabout 0.05 part of polyacrylic acid in about 4.95 part of deionizedwater. About 0.1 part of CNT is then added into the surfactant solution,and the solution is then sonicated with a high power sonicator for about1 minute at 60% output. The sonication is repeated 3 times. Theresulting CNT aqueous dispersion is observed to be uniformly coated on apiece of glass slide.

CNT/PFA coating formulation: About 17.5 part of CNT dispersion describedin paragraph [0042] above is further mixed with a PFA dispersion (22.5part) having a weight of about 38 weight percent, thereby resulting inabout 2 weight percent of CNT in PFA. The CNT/PFA dispersion is stableat room temperature over a number of days. Prior to coating, the CNT/PFAdispersion is sonicated for about 1 minute, and uniformly coated on theglass slide.

Coating and baking. the CNT/PFA coating dispersion is coated on apre-cleaned and primed silicone rubber roll by spray-coating to form alayer having approximate thickness of 30 to 40 micrometers. The primeris applied by spray-coating with a clear primer coating formulationpurchased from DuPont (990CL). The coating layer is then heated at 200°C. for 5 minutes and 345° C. for 18 minutes. The dried coatings areuniform and free of cracks, as analyzed by optical microscopic image andSEM image.

Comparative example: The PFA coating formulation is coated on thepre-cleaned silicone rubber roll by spray-coating to form an approximatethickness of 30 micrometer layer. The coating layer is then heated withthe same conditions, however the resulting coating have many cracks.

Compared to the current fluoroplastic coating materials and processes,the formulation described herein allows a wider processing window(ranging from about 330° C. to about 360° C. and from about 5 to about15 minutes to produce crack-free topcoats. Defect-free topcoats havebeen fabricated with a thickness ranges from 30 to 50 micron and showsignificantly improved mechanical properties (2× yield strength andhigher Young's Modulus) (FIG. 4( b)) compared to the topcoat without CNT(FIG. 4( a)).

Other embodiments of the present teachings will be apparent to thoseskilled in the art from consideration of the specification and practiceof the present teachings disclosed herein. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the present teachings being indicated by thefollowing claims.

1. A coating composition comprising a liquid, fluoropolymer particles,carbon nanotubes, and a dispersant, wherein the dispersant has a thermaldegradation temperature below a melting temperature of the fluoropolymerparticles.
 2. The coating composition of claim 1, wherein the liquid isselected from a group consisting of water, an alcohol, a C₅-C₁₈aliphatic hydrocarbon, a C₆-C₁₈ aromatic hydrocarbon, an ether, anester, a ketone, and an amide.
 3. A coating composition of claim 1,wherein the fluoropolymer particles are selected from the groupconsisting of polytetrafluoroethylene (PTFE); perfluoroalkoxy polymerresin (PFA); copolymer of tetrafluoroethylene (TFE) andhexafluoropropylene (HFP); copolymers of hexafluoropropylene (HFP) andvinylidene fluoride (VDF or VF2); terpolymers of tetrafluoroethylene(TFE), vinylidene fluoride (VDF), and hexafluoropropylene (HFP); andtetrapolymers of tetrafluoroethylene (TFE), vinylidene fluoride (VF2),and hexafluoropropylene (HFP).
 4. A coating composition of claim 1,wherein the carbon nanotubes are selected from the group consisting ofsingle wall carbon nanotubes and multiple wall carbon nanotubes, andwherein the carbon nanotubes have an aspect ratio of at least about 10.5. A coating composition of claim 1, wherein the carbon nanotubes arepresent in an amount ranging from about 0.1 weight percent to about 50weight percent based on the total weight of the carbon nanotubes and thefluoropolymer particles.
 6. A coating composition of claim 1, whereinthe dispersant is selected from the group consisting of a polymericamine, a polyethylene glycol, a polymeric acid, and a natural gummaterial.
 7. A coating composition of claim 6, wherein the dispersant isselected from a group consisting of a polyacrylic acid, apolymethacrylic acid, a polyethylene glycol containing surfactant, and apolyallylamine.
 8. A coating composition of claim 1, wherein the thermaldegradation temperature of the dispersant is about 100° C. to about 280°C.
 9. A coating composition of claim 1, wherein the melting temperatureof the fluoropolymer particles is from about 255° C. to about 360° C.10. A coating composition of claim 1, wherein the dispersant is presentin an amount ranging from about 10 weight percent to about 50 weightpercent of the total weight of the carbon nanotubes and the dispersant.11. A method of making a fuser member, comprising: obtaining a fusermember comprising a silicone resilient layer disposed on a substrate;providing a coating dispersion comprising a liquid, fluoropolymerparticles, carbon nanotubes, and a dispersant, wherein the dispersanthas a thermal degradation temperature below a melting temperature of thefluoropolymer particles; applying the coating dispersion over thesilicone resilient layer to form a coating layer; and heating thecoating layer, including heating the coating layer to a temperatureabove the degradation temperature of the dispersant to allow removingthe dispersant.
 12. A method of claim 11, wherein the liquid is selectedfrom a group consisting of water, an alcohol, a C₅-C₁₈ aliphatichydrocarbon, a C₆-C₁₈ aromatic hydrocarbon, an ether, an ester, aketone, and an amide.
 13. A method of claim 11, wherein thefluoropolymer particles are selected from the group consisting ofpolytetrafluoroethylene (PTFE); perfluoroalkoxy polymer resin (PFA);copolymer of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP);copolymers of hexafluoropropylene (HFP) and vinylidene fluoride (VDF orVF2); terpolymers of tetrafluoroethylene (TFE), vinylidene fluoride(VDF), and hexafluoropropylene (HFP); and tetrapolymers oftetrafluoroethylene (TFE), vinylidene fluoride (VF2), andhexafluoropropylene (HFP).
 14. A method of claim 11, wherein the carbonnanotubes are selected from the group consisting of single wall carbonnanotubes and multiple wall carbon nanotubes, and wherein the carbonnanotubes have an aspect ratio of at least about
 10. 15. A method ofclaim 11, wherein the dispersant is selected from a group consisting ofa polyacrylic acid, a polymethacrylic acid, a polyethylene glycolcontaining surfactant, a polyallylamine, and a copolymer comprisedthereof.
 16. A method of claim 11, wherein the release layer has anelectrical surface resistivity of less than about 10⁸ Ω/sq.
 17. A methodof claim 11, wherein the step of applying the dispersion over theresilient layer to form a coated substrate comprises an applicationtechnique selected from the group consisting of spray coating, painting,dip coating, brush coating, roller coating, spin coating, casting, andflow coating.
 18. A method of claim 11, wherein the heating comprises afirst step of heating the coating layer to a temperature above adegradation temperature of the dispersant to allow removing thedispersant; and a second step of heating the coating layer to atemperature above a melting temperature of the fluoropolymer particlesto melt the fluoropolymer.
 19. A method of claim 19, wherein thedegradation temperature ranges from about 150° C. to about 250° C. andthe melting temperature for fluoropolymer ranges from 255° C. to about360° C.
 20. A fuser member comprising: a substrate; a silicone layerdisposed on the substrate; and an outer layer disposed on the siliconelayer wherein the outer layer is formed from a coating dispersioncomprised of a liquid, fluoropolymer particles, carbon nanotubes, and athermally removable dispersant, wherein the thermally removabledispersant has a thermal degradation temperature below a meltingtemperature of the fluoropolymer particles.